[Talk-GB] UK coastline data

Mark Goodge mark at good-stuff.co.uk
Fri Jul 12 08:16:44 UTC 2019

On 11/07/2019 20:38, Borbus wrote:

> The mess often happens because mappers don't necessarily know what a 
> "coastline" is (I didn't before I researched it). For land-based maps 
> the coastline that is shown is generally shown is mean high water level. 
> The other "coastline" that is also shown on land-based maps is the mean 
> lower water level. The bit between these lines is the intertidal zone. 
> This is admittedly a bit less interesting, but it's certainly useful 
> when there are causeways and other features in the intertidal zone.

It's also one of the most useful from a leisure perspective, as a lot of 
popular beaches fall primarily or wholly in the intertidal zone. Take, 
for example, Hunstanton in Norfolk - at high tide the sea comes all the 
way up to the sea wall, and there is no beach as such on the town centre 
seafront. But, at low tide, there's a large expanse of sand. And, in 
between, there are differing amounts of sand visible!

FWIW, I think that both OSM and OS currently show this correctly, with 
the intertidal beach being mapped as sand (as are the sand and mud banks 
further south near Heacham and Snettisham). Google, on the other hand, 
seems to be ignoring the intertidal area completely and mapping the 
coastline according to what is visible on their own aerial imagery (for 
a good example of that, zoom into Hunstanton Sea Life Centre on Google 
maps and then switch between map and satellite view).


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